The caps (or fins) clamped by torsion against a plane face substantially parallel to the radial axis Z'Z of the blade are poor at transmitting the dynamic moments Mz existing about said radial axis whenever the two contacting faces of adjacent caps (or fins) are not exactly parallel (see FIG. 3). As a result, the function performed by the contact face which is clamped by torsion depends on its quality of manufacture and this has the drawback of giving rise to dispersion in the vibration properties of each blade when taken separately. This dispersion has an effect on the entire moving blade by modifying its resonant frequencies in an uncontrolled manner and by giving rise to a greater number of resonant frequencies which makes it difficult to avoid resonance with known excitation frequencies.
Preferred embodiments of the present invention mitigate this drawback.
SUMMARY OF THE INVENTION
The present invention provides moving blading for a steam turbine, the blading comprising blades having respective generally radial bodies provided with transverse members (e.g. caps or fins) with the transverse members on adjacent blades coming into contact (at least during rotation of the blading) over plane surfaces which are substantially parallel to the radial axes Z'Z of the blades, said contacts causing the blade bodies to twist, wherein, in addition to said contacts between adjacent transverse members, the blading includes links provided by means of additional contacts which are free to slide rectilinearly in planes corresponding to the plane of each transverse member along respective axes which are substantially perpendicular to the axis of rotation 00' of the blading, said additional contacts being situated at a relatively large distance from said contacts that give rise to twisting.
The links set up between adjacent caps (or fins) by these additional contacts have the effect that relative motion of these caps (or fins) gives rise on each of them to points A and A' (which may be distinct or which may coincide) at which friction forces f and f' contained in the plane of the caps (or the fins) occur, which friction forces have a moment .sub.-- M.sub.Z relative to the mean contact point C on the plane surface. The sum M.sub.Z +.sub.-- M.sub.Z may be different from one blade to another such that even in the extreme case where the faces clamped by torsion are incapable of transmitting the slightest moment between adjacent caps (or fins), said transmission is nevertheless provided by the .sub.-- M.sub.Z (see FIG. 3). It is important for the points A and A' to be situated as far as possible from the contact faces so as to hinder as much as possible any rotation movement of the cap (or the fin) which may occur about a spot contact point C.
In a first embodiment of the invention, the additional contacts are constituted by extensions of the caps or fins whose top faces press against the top faces of complementary cavities provided in the adjacent caps or fins.
In this case, the point A of one blade coincides with the point A' of the adjacent blade.
In a second embodiment of the invention, the additional contacts are provided by link members situated in grooves opening out into the side surfaces of the caps or fins furthest from the contacts that give rise to twisting, said members rubbing against the walls of said grooves.